1. Field of the Invention
This invention relates to striping steel slabs and ingots for the detection of inclusions, and more particularly to an improved method of and apparatus for automatically striping a hot steel slab produced in a continuous caster.
2. Description of the Prior Art
In the production of steel by a continuous casting process, the continuously cast strand is conventionally cut into slabs of predetermined length on the horizontal runout table. The individual slabs, after being weighed and marked for identification, are moved from the runout table to a storage area where they are permitted to air cool to a temperature which will enable personnel to walk over and inspect them. Depending on their size and cooling conditions, individual slabs may have to be retained in the storage area for from 18 to 36 hours after casting. Inspection is necessary to determine the extent, if any, of scarfing which may be required before further processed as by rolling, or whether a portion or all of an individual slab may have to be removed as scrap.
One inspection procedure known as striping involves a technique of using an oxygen-gas torch for scarfing a thin stripe across the top surface of the slab to evaluate the quantity and depth of alumina inclusions adjacent the surface. As is known, the outer or skin layer of a cast slab consists primarily of scale which is removed during subsequent reheating and rolling processes. The initial pass of the striping torch removes this outer skin layer in a path which may be approximately three inches wide and extend across the full width of the slab.
As the striping torch is moved along the slab surface, a molten puddle of metal moves ahead of the torch. When this molten metal comes into contact with an alumina inclusion, a visible flash is produced as the alumina particle is rapidly reduced.
In the prior art method of striping, an operator stands on the slab and moves the striping torch across its cooled surface. The torch is clamped and supported for movement on a wheeled dolly which the operator rolls along the top of the slab while observing, counting and evaluating the flashes. Alternatively, the operator may rest the torch directly on the slab and hold it at the desired angle while manually sliding it across the surface to be striped. After the torch has traversed the slab to remove the outer skin layer, the operator moves back to the starting point and makes a second pass with the torch in the same path to scarf a second thin layer of metal from the slab. In this process, the human element involves not only the ability to control movement of the torch while observing and counting the flashes, but also the ability to remember and compare the flashes on the two passes of the torch required for each stripe.
As indicated above, the material in the outer skin layer is normally removed as scale during subsequent reheating and rolling processes. The flashes in the sub-surface layer, however, may indicate the necessity for subsequent scarfing of the slab surface to remove excessive alumina inclusions which, if not removed, will show up as streaks or slivers in the surface of the steel following subsequent rolling. The removal of excessive alumina becomes more critical as steel is rolled into strip of thinner gauges. Thus, accurate counting of the flashes becomes important if the striping procedure is to be considered a reliable indication of the necessity of subsequent treatment processes such as scarfing. A comparison of the flashes observed in the first and second passes of the striping torch has been determined to be a reliable indication of the depth of inclusions which might be expected.
The prior art procedure of cooling slabs before striping is undesirable not only because of the substantial storage space required and the time and cost involved in moving the slabs to and from storage but also because much of the heat lost during cooling must be restored before subsequent rolling operations. Thus, if it can be determined that the alumina inclusions are such that scarfing will not be necessary, a slab can be moved directly from the caster runout table to the next processing step with little or no reheating required. At the same time, if the inclusions are such that scarfing is required, the slab can be sent directly to the scarfing area for processing and then transferred to the next process step. Accordingly, the primary object of the present invention is to provide an improved method and apparatus for automatically striping steel slabs without requiring an operator present on the slab to observe the torch flame during the striping process.
Another object is to provide such a method and apparatus for striping a steel slab before it has cooled following the casting process.
Another object is to provide such a method and apparatus for striping a hot steel slab on the runout table of a continuous caster at a location downstream from the slab cut-off machine.
Another object is to provide an apparatus for and method of automatically striping a hot steel slab.
Another object is to provide such an apparatus which will automatically manipulate a striping torch, optically detect and count flashes representing alumina inclusions, and provide a readout of the striping process at a station remote from the striping torch.